CMOSFET With Hybrid-Strained Channels

ABSTRACT

Disclosed is a method of manufacturing microelectronic devices including forming a silicon substrate with first and second wells of different dopant characteristics, forming a first strained silicon-germanium-carbon layer of a first formulation proximate to the first well, and forming a second strained silicon-germanium-carbon layer of a second formulation distinct from the first formulation proximate to the second well. Capping and insulating layers, gate structures, spacers, and sources and drains are then formed, thereby creating a CMOS device with independently strained channels.

RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No. 10/922,087 filed Aug. 19, 2004, and entitled, “CMOSFET With Hybrid-Strained Channels,” which is hereby incorporated by reference in its entirety.

BACKGROUND

Formation of a semiconductor transistor typically comprises a doped substrate featuring a source and a drain bounded by dielectric regions, a gate dielectric layer, and a gate. One method of increasing the performance of that composition is enhancement of carrier mobility by introduction of a strained channel beneath the gate and between the source and drain.

The conventional approach to creating this strained channel is the replacement of a silicon substrate with bulk silicon-germanium, which is graded so as to produce relaxed silicon-germanium at the wafer surface. The silicon-germanium is then covered (capped) with epitaxial silicon. The difference in lattice constants between the silicon cap and the underlying silicon-germanium produces tensile stress in the silicon, and thus more carrier mobility in the silicon cap. A disadvantage with this approach is that the substitution of silicon substrate with relaxed silicon-germanium is both expensive and time-consuming. A further disadvantage is that dislocations in the silicon-germanium lattice are difficult to control and can spread into the strained silicon layer, degrading that layer and hampering performance. The higher the level of defect control, the more expensive the process becomes.

Another approach is capping a doped silicon substrate with an epitaxial layer of strained silicon-germanium. As in the conventional approach, the difference in lattice constants between the silicon-germanium and the silicon produces stress in the capped layer. Since the layers are reversed from the conventional approach, the silicon is relaxed while the silicon-germanium is compressively stressed. The strain produces the same benefit of enhanced carrier mobility. Unlike the conventional approach, this process is not expensive since the growth of a thin layer of stressed silicon-germanium is cheaper and less time-consuming than the growth of a thick layer of relaxed silicon-germanium. A disadvantage is that this method only improves p-channel metal oxide semiconductor (PMOS) performance, but degrades n-channel metal oxide semiconductor (NMOS) performance. An alternative is the use of a thin silicon-carbon layer instead of a silicon-germanium layer. The difference in lattice constants for the silicon-carbon on silicon configuration puts tensile, rather than compressive, stress on the silicon-carbon cap. However, this method only improves NMOS performance, but degrades PMOS performance.

It is desired to provide strained channels that improve different types of channels and devices, such as complementary metal oxide semiconductor (CMOS) devices.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increase or reduced for clarity of discussion.

FIG. 1 is a cross-sectional view of at least a portion of one embodiment of a microelectronic device in an intermediate stage of manufacture according to aspects of the present disclosure.

FIG. 2 is a cross-sectional view of the device shown in FIG. 1 in a subsequent stage of manufacture.

FIG. 3 is a cross-sectional view of the device shown in FIG. 2 in a subsequent stage of manufacture.

FIG. 4 is a cross-sectional view of the device shown in FIG. 1 in a subsequent stage of manufacture.

FIG. 5 is a cross-sectional view of the device shown in FIG. 4 in a subsequent stage of manufacture.

FIG. 6 is a cross-sectional view of the device shown in FIG. 3 or FIG. 5 in a subsequent stage of manufacture.

FIG. 7 is a cross-sectional view of the device shown in FIG. 6 in a subsequent stage of manufacture.

FIG. 8 is a cross-sectional view of the device shown in FIG. 7 in a subsequent stage of manufacture.

FIG. 9 is a cross-sectional view of at least a portion of one embodiment of an integrated circuit according to aspects of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments or examples for implementing different features of various embodiments. Specific examples of components and arrangements are described below only to simplify the disclosure. These are merely examples and are not intended to be limiting. Additionally, the present disclosure may repeat reference numbers and/or letters in the various examples. Such repetition is for the purposes of simplicity and clarity, and does not itself dictate a relationship between the various embodiments and/or configurations discussed herein. Moreover, the formation of a first feature proximate to a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact as well as embodiments in which additional features may be formed interposing the first and second features such that the first and second features may not be in direct contact.

Unless specified otherwise, layer addition may comprise chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), physical layer deposition, sputtering, spin-on-coating, and/or other additive processes. Unless specified otherwise, layer removal may comprise chemical mechanical polish (CMP), wet etch, dry etch, and/or other removal processes. Doping may comprise implantation, in situ growth, and/or other dopant addition processes.

FIG. 1 illustrates a sectional view of at least a portion of one embodiment of a microelectronics device 100 in an intermediate stage of manufacture according to aspects of the present disclosure. In one embodiment, the device may be fabricated on substrate 101 having doped well regions 102 a and 102 b. The substrate 101 may comprise silicon, monocrystalline silicon, gallium-arsenide, and/or other materials. The differently doped well regions 102 a and 102 b may comprise any combination of substrate and one or more impurities in two different quantities in two different regions. In one embodiment, the differently doped well regions may comprise 102 a being a p-type region, indicating doping with a species such as boron, and 102 b being an n-type region, indicating doping with species such as arsenic and/or phosphorous. In another embodiment, the differently doped well regions may comprise 102 a being a p⁺ region, indicating a high amount of doping with a species such as boron, and 102 b being a p⁺⁺ region, indicating a very high amount doping with a species such as boron. Formation of well regions is well known in the art, and one of ordinary skill may appreciate that certain combinations of different well regions are needed for certain devices.

In one embodiment, doped regions 102 a and 102 b may be separated by isolation structures 104. The isolation structures 104 may comprise a dielectric material such as silicon-oxide (SiO₂), silicon-nitride (Si₃N₄), and/or other low-k dielectric or electrically insulating materials. Formation of the isolation structures 104 may comprise local oxidation of silicon (LOCOS), shallow trench isolation (STI), and/or other methods.

FIGS. 2 and 3 illustrate one method for forming a strained channel that works with different types of doped regions. Referring to FIG. 2, a first strained layer 206 a by forming a hard mask 208 b over one well 102 b, while leaving the other well 102 a uncovered. The hard mask 208 b may comprise silicon-nitride, silicon-oxygen-nitride (SiON), and/or other deposition and/or implant resistive materials.

In one embodiment, the first strained layer 206 a may comprise selective epitaxial growth (SEG) in areas where the substrate 101 is not covered by the hard mask 208 b—which includes well 102 a in the present example. The strained layer 206 a can be formed using silane and/or disilane, germane, methane, and an etchant such as hydrochloric acid as reagents. After formation of the strained layer 206 a, the hard mask 208 b may be removed. If the embodiment contains isolation structures 104, the materials used for the hard mask 208 b and the isolation structures 104 may be different to allow for selective removal and/or other processing at subsequent steps.

FIG. 3 illustrates a subsequent step to FIG. 2 in which a second hard mask 308 a is formed over the first strained layer 206 a. The second hard mask 308 a may be similar in construction to the first hard mask 208 b of FIG. 2. The second hard mask 308 a permits formation of a second SEG strained layer 306 b proximate to the second doped well 102 b. In an embodiment where the second strained layer 306 b is silicon-germanium-carbon, the layer may be formed using silane and/or disilane, germane, methane, and an etchant such as hydrochloric acid as reagents. After formation of the strained layer 306 b, the hard mask 308 a may be removed.

In some embodiments, the strained layers 206 a and 306 b may be tri-elemental, comprising silicon, germanium, and carbon in formulation, such as according to the following equation: Si_(1−x−y)Ge_(x)C_(y).   (1) However, the fact that a tri-elemental layer substantially comprises three elements does not preclude composition of additional elements, be they impurities or desired species. The tri-elemental strained layers 206 a and 306 b may also comprise species added or removed by any subsequent processing, such as implant doping, to form a source and drain. Further, a tri-elemental layer may comprise substantially two elements such that it functions as a di-elemental layer, for example silicon-germanium-carbon with a only trace amount of carbon wherein y from equation (1) is nearly nil, leaving essentially Si_(1−x)Ge_(x). This type of formulation allows for easier process modification to increase the relative amount of the trace third element, whereas use of a simple di-elemental layer might require process and tool redesign to achieve such an increase in the trace element. However, a di-elemental layer may be used when proper for the process and/or process tools.

In an embodiment where the strained tri-elemental layer 206 a is silicon-germanium-carbon grown on the p-well 102 a (in the present example), the germanium content may be about twenty to thirty mol percent. Applied to equation (1), x should be at least ten times y, such as: Si_(0.74)Ge_(0.25)C_(0.01). As y approaches nil, the composition is essentially Si_(1−x)Ge_(x). In embodiments where x is greater than ten times y, the lattice constant of the strained silicon-germanium-carbon layer 206 a is higher than the lattice constant of the underlying substrate 102 a, producing compressive strain in the silicon-germanium-carbon layer 206 a.

In an embodiment where the a strained tri-elemental layer 306 b is silicon-germanium-carbon grown on a well 102 b (in the present example), the carbon content may be about two to three mol percent. Applied to equation (1), x should be less than ten times y, such as: Si_(0.875)Ge_(0.1)c_(0.025). As x approaches nil, the composition is essentially Si_(1−y)C_(y). In embodiments where x is less than ten times y, the lattice constant of the strained silicon-germanium-carbon layer 306 b is lower than the lattice constant of the underlying n-type substrate 102 b, producing tensile strain in the silicon-germanium-carbon layer 306 b.

In order to be of distinct formulations, the tri-elemental strained layers 206 a and 306 b should have different lattice constants. In one embodiment, the distinct tri-elemental strained layer 206 a may comprise silicon-germanium-carbon wherein carbon concentration is less than ten times germanium concentration and the distinct tri-elemental strained layer 306 b being silicon-germanium-carbon wherein carbon concentration is greater than ten times germanium concentration. In another embodiment, the distinct tri-elemental strained layer 206 a may comprise substantially silicon-germanium and the distinct tri-elemental strained layer 306 b may comprise substantially silicon-carbon.

In some embodiments, the SEG strained tri-elemental layers 206 a and 306 b may be further processed to add and/or remove species with the hard masks 208 b and 308 a in place, with the hard masks 208 b and 308 a removed, or in combination. A process to add species may comprise implantation. Sacrificial layers such as silicon-oxide may be used to prevent surface damage caused by implantation. A process to remove species may comprise a leaching agent or layer.

FIGS. 4 and 5 illustrate another method for forming a strained channel that works with different types of doped regions, such as is disclosed in FIG. 1. It is understood that the steps discussed above with FIGS. 2 and 3 can be used on some devices while the steps discussed below with FIGS. 4 and 5 can be used on other devices on the same wafer.

Referring to FIG. 4, a layer 406 may be formed over both the wells 102 a and 102 b. Formation of layer 406 may comprise SEG, non-selective epitaxial growth, and/or other means. In the present embodiment, the layer 406 includes the three elements silicon, germanium, and carbon.

After layer 406 has been formed, a hard mask 408 b covers both well 102 b and a portion 406 b of layer 406 while leaving a portion 406 a uncovered. The hard mask 408 b may comprise silicon-nitride, silicon-oxygen-nitride, and/or other deposition and/or implant resistive materials. If the embodiment contains isolation structures 104, the materials used for the hard mask 408 b and the isolation structures 104 may be different to allow for selective processing at subsequent steps.

Once the hard mask 408 b is in place, subsequent processing can be performed to add species to and/or to remove species from layer 406 a to produce the chemical formulation desired to achieve a certain lattice structure. For example, more or different materials can be implanted, thus changing layer 406 a into something similar to tri-elemental strained layer 206 a, discussed above. In an embodiment where the tri-elemental strained layer 206 a is silicon-germanium-carbon, the implanted species may comprise germanium. Sacrificial layers such as silicon-oxide may also be used to prevent surface damage caused by implantation. In another embodiment, a process to remove species from the layer 406 a may comprise a leaching agent or layer. After formation of the tri-elemental strained layer, now referred to as layer 506 a (FIG. 5), the hard mask 408 b may be removed.

Referring to FIG. 5, a hard mask 508 a covers both well 102 a and tri-elemental strained layer 506 a while leaving the other well 102 b and layer 406 b uncovered. The hard mask 508 a may comprise silicon-nitride, silicon-oxygen-nitride, and/or other deposition and/or implant resistive materials. If the embodiment contains isolation structures 104, the materials used for the hard mask 508 a and the isolation structures 104 may be different to allow for selective processing at subsequent steps. Subsequent processing to add species to and/or to remove species from layer 406 b may be used to produce the chemical formulation desired to achieve a certain lattice structure in the layer 406 b, thus changing layer 406 b into something similar to tri-elemental strained layer 306 b, and distinct from tri-elemental strained layer 506 a described in the preceding paragraph.

A process to add species may comprise implantation. In an embodiment where the tri-elemental strained layer is silicon-germanium-carbon, the implanted species may comprise carbon. Sacrificial layers such as silicon-oxide may be used to prevent surface damage caused by implantation. A process to remove species may comprise a leaching agent or layer. After formation of tri-elemental strained layer, the hard mask 508 a may be removed. Although this embodiment illustrates treatment of layer 406 a first, one of skill in the art will recognize that layer 406 b may be treated first by covering layer 406 a with hard mask 508 a. Other embodiments may comprise alternating treatments wherein hard masks 408 b and 508 a are formed and removed more than once. Still other embodiments may comprise processes that affect both layers 406 a and 406 b or intermediaries.

FIG. 6 illustrates one embodiment that may be formed using either the methods described with reference to FIGS. 2 and 3 or with reference to FIGS. 4 and 5. A first tri-elemental strained layer 206 a (similar to layer 506 in FIG. 5) of one formulation is formed over doped region 102 a, and a second tri-elemental strained layer 306 b of a formulation distinct from tri-elemental strained layer 206 a is formed over differently doped region 102 b.

FIG. 7 illustrates subsequent processing in which the tri-elemental strained layers 206 a and 306 b may be capped with layer 710 and/or insulating layer 712. Capping layer 710 may comprise silicon. Insulating layer 712 may comprise silicon-oxide. In some embodiments, capping layer 710 may help to reduce stress between the tri-elemental strained layers 206 a and 306 b and subsequent insulating layer 712. In an embodiment where capping layer 710 is silicon and insulating layer 712 is silicon-oxide, capping layer 710 may serve as a silicon source for insulating layer 712. In some embodiments, capping layer 710 may prevent undesirable environmentally-induced oxidation of strained tri-elemental layers 206 a and 306 b. However, such oxidation may not occur in embodiments where the substrate never contacts an oxygenated atmosphere.

In a transistor embodiment, gate structures 714 may be formed on the insulating laye 712 r. Formation of gate structures 714 is well-known in the art. Gate structure 714 materials may comprise doped or undoped silicon or polysilicon, and may be capped with a more conductive material such as tungsten, aluminum, copper, an alloy such as tungsten-silicide, or any other conductive or semiconductive material or combination of such materials. Representation in the drawing of gate structure 714 as a single layer does not preclude composition of multiple layers. In an embodiment where well region 102 a is PMOS, well region 102 b is NMOS, and there are gate structures 714 over both wells, a CMOS transistor is formed. In another embodiment, a mask may be used to form gate structures 714 proximate to only one well area, forming isolated transistors.

FIG. 8 illustrates further processing in which insulating structures 812 a/812 b and spacers 816 a/816 b may be formed around gate structures 714. Formation of insulating structures 812 a/812 b and spacers 816 a/816 b is well-known in the art. Insulating structures 812 a/812 b may have a width substantially similar to the width of gate structures 714 as shown by structure 812 a or substantially similar to the width of spacers 816 b as shown by structure 812 b. The spacers 816 may comprise one or more layers of silicon-oxide, silicon-nitride, silicon-oxygen-nitride, and/or other materials. The spacers 816 a/ 816 b may independently or collectively be employed as a mask during subsequent processing to remove at least portions of insulating layer 712 as shown by structure 812 b.

In one embodiment, the spacers 816 a/816 b may act as a mask or pattern for implantation of dopants such as boron, phosphorous, arsenic, and/or other materials into substrate wells 102 a and 102 b, strained layers 206 a and 306 b, and capping layer 710 to create sources and drains 818 and channel region 820. In another embodiment, a photoresist mask may be used to implant dopants into only certain wells. Subsequent diffusion, annealing, and/or any other electrical activation processes may be employed to attain a desired doping profile. In some embodiments, the sources and drains 818 may not have similar geometric shapes or compositions. For example, the thicknesses of the sources and drains 818 relative to the sum of the layers 102 a, 102 b, 206 a, 306 b, and 710 may differ, or the widths of the sources and drains 818 and the width of the gate structure 714 may differ. In one embodiment, the sources and drains 818 may be implanted before spacer 816 a formation but after formation of isolation structure 812 a in order to produce a more narrow channel 820.

FIG. 9 illustrates an integrated circuit 922 in which the device 100 described above may be implemented. For example, the circuit 922 includes a plurality of microelectronic devices 924, one or more of which may be substantially similar to the device 100 shown in FIG. 8.

The integrated circuit 922 may also include interconnects 926 extending along and/or through one or more dielectric layers 928 to the devices 924. The interconnects 926 may comprise tungsten, aluminum, copper, and/or other materials. The interconnects 926 may further comprise a barrier metal layer between the bulk interconnect material and the dielectric layers 928. The barrier metal layer may comprise tantalum, titanium, titanium-nitride, tungsten, tungsten-silicide, tungsten-nitride, tantalum-silicon-nitride, and/or other suitable materials. The dielectric layers 928 may comprise silicon-oxide, carbon-doped silicon-oxide, fluorine-doped silicon-oxide, fluorosilicate glass (FSG), borophosphosilicate glass (BPSG), spin-on-glass (SOG), and/or any other low-k material.

Thus, the present disclosure provides a method of manufacturing a microelectronic device including forming first and second tri-elemental strained layers of distinct formulations over differently doped substrate.

The foregoing has outlined features of several embodiments according to aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

1. A method of manufacturing a microelectronic device comprising: forming a silicon substrate with first and second wells of different dopant characteristics; forming a first epitaxial silicon-germanium-carbon layer of a first formulation proximate to the first well; and forming a second epitaxial silicon-germanium-carbon layer of a second formulation distinct from the first formulation proximate to the second well.
 2. The method of claim 1 wherein the first epitaxial silicon-germanium-carbon layer of a first formulation is formed directly on top of the first well.
 3. The method of claim 1 wherein the first second epitaxial silicon-germanium-carbon layer of a second formulation is formed directly on top of the second well.
 4. The method of claim 1 further comprising: forming a hard mask over one of the wells.
 5. The method of claim 1 wherein a dopant characteristic in the first well is n-type and a dopant characteristic in the second well is p-type, and further comprising: forming isolation regions in the top portion of the silicon substrate with a shallow trench process; forming at least one hard mask over one of the wells thereby selectively forming the first epitaxial silicon-germanium-carbon layer wherein the formulation comprises more than twenty mol percent germanium over the first well and the second epitaxial silicon-germanium-carbon layer wherein the formulation comprises more than two mol percent carbon over the second well; forming a silicon capping layer; forming an insulator layer; and forming a gate structure proximate to the first and second wells.
 6. A method of manufacturing a microelectronic device sequentially comprising: forming a silicon substrate with first and second wells of different dopant characteristics; forming an epitaxial layer of a first formulation over the first and second wells; masking a first portion of the epitaxial layer overlying the first well; modifying a second portion of the epitaxial layer overlying the second well to a second formulation. 